Hello, folks. I have a '66 122 with an M41, which I'm just about ready to put back on the road after three years of restoration. Here's my problem: when I start the engine and let it idle, the needle on the temperature gauge heads over to the far right in no time at all. When I've driven the car (three jaunts around town so far, about 10 minutes on the road at most) the needle never moves to the left of "H".

The car has a new thermostat, new radiator hoses and heater hoses, and I had the radiator boiled out. The radiator is from a later model 122 with the expansion tank.

I haven't noticed the engine missing or any steam coming out, but when I park the car and pop the hood, I see that coolant is coming out of the overflow tank's cap, and I hear what sounds like -- well, like boiling water.

Having eliminated what I would think are the most obvious causes -- silted-up radiator and bad thermostat -- what should I look at next?

Thanks,
Dave LaChance

Thanks to everyone for your help. And the culprit was... the thermostat! It was in the right way, but it failed the pan-of-boiling-water-on-top-of-the-stove test. Didn't open up even the slightest bit.

Without the thermostat, the engine runs well within the normal temp range.

I guess the moral is don't overlook the obvious. It should have occurred to me to suspect the thermostat, but I discounted that idea because the part was new. New parts aren't necessarily good parts, are they? ;>)

Thanks again!

Dave LaChance

I'm always suspect first of thermostats, as they are majic. I hate to ask, but are you *certain* you don't have it in there backwards?

I'd start by removing the thermostat, and running it without and see what it does. If it runs cool, you have your culprit.

-Matt
--
-Matt '70 145s, '65 1800s, '66 122s wagon, others inc. '53 XK120 FHC

Aidan mentioned it in passing but if you have checked everything else and
your thermostat IS opening as advertised, you should indeed check your
ignition timing. With everything hooked up it should be around 20° before
TDC at idle. If not, it will overheat the exhaust and also the engine as
well as reduce power output substantially.

Dave;

Only after your certain the engine is REALLY running hot do you need to look into you cooling sys. I suggest the first thing you do is verify the calibration of your temp guage, so that you know you can believe what its indicating also. Remove sensing bulb, immerse in boiling water, note reading of gauge with respect to calibration marks.


See also: http://www.intelab.com/swem/service%20notes.htm#Gauges

Cheers

I'm sorry but I do not agree, Ron (hope that is ok..)

The temp gauge for the 120's are "never" showing too much, if they fail, they mostly do that by not showing anything at all. (usally due to leak of ether in the tiny tube from sensor-bulb to gauge)

Anyway, they surdently don't show too much AND collingsystem sounds like boiling water - and boiling water should never accure in any car at all.

If the temp gauge goes all the way to the right and stay there, I would more say, that the temp gauge is working just as is should. And in this case, showing that something is wrong!

To check if cooling system is not function as should still it's even easier than removing the gauge from the back of the speedometer,

-remove thermostat, mount thermostat-housing and run engine. Change? If so, there you go!

actually I have had 2 temp gages read consistently too hot when the engine was not. It is not a failure per say as they are still reading the temp, they just register too high.
--
Patrick, '68 220, '83 245, '92 Eurovan (work truck).

Hi,

Probably too obvious but if the system is filled without the heater set to 'hot' then you could easily have an airlock. Other possibilities are your waterpump, fan belt tension and head gasket. Fan belt tension is easy to check, waterpump should show coolant movement with the rad cap off and the engine revving (though that doesn't mean that the pump is working perfectly, just that its pumping some water) and you may need to check your cylinder compression to check for a leaking head gasket (also checking for oil in the water, water in the oil and white exhaust vapour).

Assume timing is ok?

Start with the easy one - the possible airlock and work up from there.

Aidan

--
1967 131, 1969 131, 1973 Triumph GT6

Hi Dave,

Try this:

If you feel the radiatorhoses when engine is hot:

1)Is the upper hose hot, but the lower hose not? (if so, dubble-check if radiator is only hot on top and not on bottom)
-if so, it's a bad thermostat!
Have you by accident put the thermostat upside down? (Anyway, it easy to check!)


2)If radiator-cap is removed while engine runs, do you se bubbles and "boiling"-like action in coolant? (air-bubbles = bad, but normal movement just indicates that water is moving and waterpump is doing its job)
-if so, there could be a worn gasket (don't know the right translation, but gasket between head/top and cylinders)

The signs you are giving deffently is overheating and my first guess would be thermostat - as if the water doesn't move freely and therefor boils up quickly. Very easy to check, as I suggest, but even more easy to just remove the thermostat, let the rubbergasket sit, and drive 10 minutes again, any difference??

Reading your message for the third time, there is no doubt in my mind.. Do as I suggest, remove thermostat, run engine, same problem? I would almost bet a cool sixpack...

Hope my english is ok..
/Soren